1. Technical Field
The present invention relates to an apparatus and method for checking a network synchronization clock signal in a communication system.
2. Related Art
In a typical network synchronization system, a communication system performs an operation in synchronization with a network synchronization clock signal received from a switching network.
The communication system includes a circuit which determines whether the network synchronization clock signal is normal or not, and outputs the result. That is, the communication system analyzes whether the network synchronization clock signal is normal or not, and is synchronized with a clock signal determined to be a normal network synchronization clock signal.
A network synchronization clock checking apparatus of the communication system includes a coefficient adjusting circuit and a multivibrator.
In this regard, the coefficient adjusting circuit is embodied by a resistor and a condenser. This coefficient adjusting circuit generates a predetermined coefficient through the resistor and the condenser so that a clock signal, which is supposed to descend from ‘1’ to ‘0,’ remains ‘1.’
The multivibrator receives a network synchronization clock signal received by the communication system, checks the network synchronization clock signal, and outputs the result.
The network synchronization clock checking apparatus having the above-described circuit configuration operates the coefficient adjusting circuit, and generates a predetermined coefficient until a network synchronization clock signal input to the multivibrator is lowered from ‘1’ to ‘0’ and then elevated from ‘0’ to ‘1’ again, so that the network synchronization clock signal input to the multivibrator remains ‘1.’ That is, the network synchronization clock checking apparatus allows the multivibrator to keep outputting ‘1’ when the network synchronization clock signal is normally inputted to the multivibrator without a break.
Furthermore, the network synchronization clock checking apparatus allows the multivibrator to output ‘0’ when the network synchronization clock signal is abnormally interrupted.
However, the network synchronization clock checking apparatus of the communication system senses only a level transition made by the network synchronization clock signal inputted to the multivibrator, and determines whether the network synchronization clock signal is normal or not. Accordingly, even if the input network synchronization clock signal is abnormal, the network synchronization clock checking apparatus may determine that the clock signal is normal on the basis of a level transition.
Moreover, because the coefficient adjusting circuit of the network synchronization clock checking apparatus includes the resistor and the condenser, an error in the coefficient obtained through the resistor and the condenser may occur due to the defects and erroneous values of respective components.